The present invention relates to a system for the extracorporeal circulation of the blood for a patient undergoing an operation on the lung or heart to refresh the blood of the patient and always circulate the blood through the body in place of the lungs and heart of the patient.
Systems for extracorporeally circulating the blood comprise a blood withdrawing line for drawing off the venous blood from the patient, an artificial lung provided on the line, a reservoir for the withdrawn blood, a blood supply line for feeding the blood from the reservoir to the artery of the patient, and a blood supply pump provided on the blood supply line and serving as an exteriorly positioned heart. With such systems, it is most critical to maintain the amount of the blood withdrawn from the body of the patient in balance with the supply of the blood to the body to keep the amount of the blood circulated through the body constant at all times. In controlling the amount of blood circulation through the body, bleeding from the site operated on, etc. must also be considered since bleeding reduces the amount of blood in the body. Conventionally the amount of blood circulation through the body is controlled by the operator through manual procedures for driving the blood withdrawing pump and blood supply pump and replenishing the blood reservoir with transfusion blood. This mode of control involves many items of manipulation, and the system must be controlled itemwise promptly based on immediate judgment while watching incessantly changing conditions of the patient, i.e. arterial and venous blood pressures, measurement of amount of bleeding, amount of blood in the reservoir and electrocardiogram. Thus the operator must be trained for controlling the system. Additionally the operator suffers from much fatigue when the operation takes a prolonged period of time.